1 .TH g_bar 1 "Thu 26 Aug 2010" "" "GROMACS suite, VERSION 4.5"
3 g_bar - calculates free energy difference estimates through Bennett's acceptance ratio
10 .BI "\-oi" " barint.xvg "
11 .BI "\-oh" " histogram.xvg "
12 .BI "\-g" " energy.edr "
14 .BI "\-[no]version" ""
26 \&g_bar calculates free energy difference estimates through
27 \&Bennett's acceptance ratio method.
28 \&Input option \fB \-f\fR expects multiple dhdl files.
29 \&Two types of input files are supported:
31 \&* Files with only one y\-value, for such files it is assumed
32 \&that the y\-value is dH/dlambda and that the Hamiltonian depends
33 \&linearly on lambda. The lambda value of the simulation is inferred
34 \&from the subtitle if present, otherwise from a number in the
35 \&subdirectory in the file name.
38 \&* Files with more than one y\-value. The files should have columns
39 \&with dH/dlambda and Delta lambda. The lambda values are inferred
41 \&lambda of the simulation from the legend of dH/dlambda
42 \&and the foreign lambda's from the legends of Delta H.
45 \&The lambda of the simulation is parsed from dhdl.xvg file's legend
46 \&containing the string 'dH', the foreign lambda's from the legend
47 \&containing the capitalized letters 'D' and 'H'. The temperature
48 \&is parsed from the legend line containing 'T ='.
51 \&The free energy estimates are determined using BAR with bisection,
52 \&the precision of the output is set with \fB \-prec\fR.
53 \&An error estimate taking into account time correlations
54 \&is made by splitting the data into blocks and determining
55 \&the free energy differences over those blocks and assuming
56 \&the blocks are independent.
57 \&The final error estimate is determined from the average variance
58 \&over 5 blocks. A range of blocks numbers for error estimation can
59 \&be provided with the options \fB \-nbmin\fR and \fB \-nbmax\fR.
62 \&The results are split in two parts: the last part contains the final
63 \&results in kJ/mol, together with the error estimate for each part
64 \&and the total. The first part contains detailed free energy
65 \&difference estimates and phase space overlap measures in units of
66 \&kT (together with their computed error estimate). The printed
69 \&* lam_A: the lambda values for point A.
71 \&* lam_B: the lambda values for point B.
73 \&* DG: the free energy estimate.
75 \&* s_A: an estimate of the relative entropy of B in A.
77 \&* s_A: an estimate of the relative entropy of A in B.
79 \&* stdev: an estimate expected per\-sample standard deviation.
82 \&The relative entropy of both states in each other's ensemble can be
83 \&interpreted as a measure of phase space overlap:
84 \&the relative entropy s_A of the work samples of lambda_B in the
85 \&ensemble of lambda_A (and vice versa for s_B), is a
86 \&measure of the 'distance' between Boltzmann distributions of
87 \&the two states, that goes to zero for identical distributions. See
88 \&Wu & Kofke, J. Chem. Phys. 123 084109 (2009) for more information.
92 \&The estimate of the expected per\-sample standard deviation, as given
93 \&in Bennett's original BAR paper:
94 \&Bennett, J. Comp. Phys. 22, p 245 (1976), Eq. 10 gives an estimate
95 \&of the quality of sampling (not directly of the actual statistical
96 \&error, because it assumes independent samples).
100 .BI "\-f" " dhdl.xvg"
101 .B Input, Opt., Mult.
108 .BI "\-oi" " barint.xvg"
112 .BI "\-oh" " histogram.xvg"
116 .BI "\-g" " energy.edr"
117 .B Input, Opt., Mult.
122 Print help info and quit
124 .BI "\-[no]version" "no "
125 Print version info and quit
127 .BI "\-nice" " int" " 0"
131 View output xvg, xpm, eps and pdb files
133 .BI "\-xvg" " enum" " xmgrace"
134 xvg plot formatting: \fB xmgrace\fR, \fB xmgr\fR or \fB none\fR
136 .BI "\-b" " real" " 0 "
139 .BI "\-e" " real" " \-1 "
142 .BI "\-temp" " real" " \-1 "
145 .BI "\-prec" " int" " 2"
146 The number of digits after the decimal point
148 .BI "\-nbmin" " int" " 5"
149 Minimum number of blocks for error estimation
151 .BI "\-nbmax" " int" " 5"
152 Maximum number of blocks for error estimation
154 .BI "\-nbin" " int" " 100"
155 Number of bins for histogram output
160 More information about \fBGROMACS\fR is available at <\fIhttp://www.gromacs.org/\fR>.